WiMAX, short for worldwide interoperability for microwave access, is currently defined by the Institute of Electrical and Electronics Engineers, or IEEE, 802.16-series specification. The advanced air interface standard is defined under 802.16m.
Packets known as service data units (SDUs) travel wirelessly between a transmitter and a receiver, such as between a base station and a mobile station, using the advanced air interface standard. Sometimes, these SDUs are fragmented into two, three, or hundreds of fragments before transmission. A fragmentation state machine at the transmitter and a defragmentation state machine at the receiver process these fragmented SDUs.
Currently under 802.16m, if a first SDU, SDU1, is being fragmented, a second, higher-priority SDU, SDU2, would have to wait in queue until all the fragments of SDU1 have been transmitted before SDU2 may be fragmented and transmitted. Particularly where large, low-priority SDUs are transmitted, this leads to undesirable results. For example, a power control request, which involves only a few bytes, is unprocessed while waiting for a very large management message, such as is used with PKM (about two Kbytes) to be processed. The power control message may be delayed indefinitely while the large PKM message is being fragmented and transmitted.
Also, as currently defined under the 802.16m standard, SDUs are dropped under certain operating conditions, namely, for non-automatic repeat request (non-ARQ) media access controller (MAC) connections that only use hybrid automatic repeat request (HARQ). “Upon loss, the receiver shall discard all SDU fragments on the connection until a new first SDU fragment is detected . . . ”. HARQ operations may temporarily miss a burst that contains some fragment of a SDU because HARQ does not guarantee in-order delivery. If the 802.16m standard does not define a mechanism to restore the order of the protocol data units (PDUs)/bursts before such a defragmentation mechanism, it will drop SDUs even though all of its fragments are correctly received (just not in order). This is especially crucial for MAC management connections where ARQ is not used and only HARQ is used.
Thus, there is a continuing need for a method to overcome the shortcomings of the prior art.